1. Field of the Invention
The present invention relates to a device for detecting an obstacle located backward of an automotive vehicle, especially, a vehicle such as a pickup truck.
2. Description of Related Art
Examples of a device for detecting obstacles located around an automobile are disclosed in JP-A-2002-323560 and JP-A-2002-372585. In such a device, ultrasonic waves are transmitted from an on-board transmitter toward obstacles, and obstacles are detected by receiving waves reflected by the obstacles. When the obstacles are detected, a driver is notified by a buzzer or the like.
When this type of a transmitter is mounted on a vehicle such as a pickup truck that has a loading space at a rear side of the vehicle and a tailgate for closing the loading space, the transmitted ultrasonic waves will be reflected by the tailgate if the tailgate is open. This may lead erroneous detection of the backward obstacles. This situation often occurs when the vehicle is driven backward while keeping the tailgate open for loading goods on the loading space. It is also known to use electromagnetic waves such as infrared waves for this purpose in place of the ultrasonic waves. The same problem is involved when the electromagnetic waves are used for detecting the obstacles.